Environmental chemicals, particularly hydrocarbons, cause disease themselves and may make organisms more susceptible to infectious disease as well. It is proposed to study 3 animal species as models and show how hydrocarbons adversely affect defense mechanisms. The hard clam (Mercenaria mercenaria), blue crab (Callinectes sapidus), and mummichog (Fundulus heteroclitus) will be exposed chronically to nonlethal concentrations of phenol, naphthalenes, and water soluble petroleum extracts. In the clam effects on epithelial surfaces will be examined histologically (including ultrastructure), phagocytosis by hemocytes and intracellular digestion will be measured as will changes in hemolymph protein. In the crab damage to gills will be assessed by light and electron microscopy, hemocyte function assayed and hemolymph protein assayed by electrophoresis. These two species lack the ability to form immunoglobulins, thus offering unique opportunities to study the effect of chemicals on nonspecific defense mechanisms. Treated fish will be assayed for their ability to reject scale transplants and to form immunoglobulins. Other physiological parameters to be measure include blood cortisol concentrations, hematocrit, blood cell and protein composition. The relative importance of epithelia, phagocytes, and nonspecific humoral factors and how they may be repressed by hydrocarbons will be clarified. Mechanisms of nonspecific as well as specific humoral and cellular immunity in fish will be clarified.